In ophthalmological therapy for the eye with laser light, the frequent demand arises for combining a laser impact beam and an object illumination and to direct them at the eye. In the event that the laser impact beam exhibits a wavelength outside the visual range of the spectrum, an additional visible aiming beam must be directed coaxially with the impact beam toward the eye in order to mark the location of the effect of the impact beam for the physician.
Since the illumination light should be transferred into the eye as complete as possible and without color distortion, substantial efforts have been required for such a combining of beams. For example, in DE 198 16 302 a beam splitter/recombiner is equipped with special reflection coatings in order to join the various wavelengths of the laser light and/or illumination light. Said coatings have a complicated structure and are difficult to manufacture, particularly when laser lights of varying wavelengths (e.g., 488 nm, 514 nm, 532 nm, 561 nm, 635 nm, and 659 nm, as commonly used in applied ophthalmology) are to be applied. Since the coatings have to be permeable at least for the wavelengths designated for the lasers, distortions of the illumination light occur because said wavelengths are not reflected.
Therefore, U.S. Pat. No. 6,394,603 suggests the use of a polarization beam splitter/recombiner with appropriate reflection coatings. This device is also difficult to manufacture and, furthermore, special demands are put on the light sources and optical elements within the beam path in order to produce and/or maintain the respective polarization.
In DE 100 31 414 of the applicant, a solution is described which forgoes the elaborate coating of the beam recombiner, whereby a plane parallel plate is used which is positioned at the Brewster's angle to the incident laser beam. However, this solution also works solely for polarized light and therefore exhibits the same disadvantages as the one previously described.